The source of the mysterious noise in 'Leave the World Behind' is never explained but here are some real-life weapons similar to it

• In Netflix's "Leave the World Behind," the protagonists are attacked by a mysterious noise.
• The noise causes intense pain and is strong enough to shatter glass.

Warning: spoilers ahead…

In the Netflix film "Leave the World Behind," an adaption of Rumaan Alam's book of the same name, the US comes under siege by an unknown entity, starting with a cyberattack that disables all communications and transportation and — later — a loud, sharp noise intense enough to shatter glass and, inexplicably, cause vomiting and loss of teeth.

This noise is all part of a mysterious plot to destabilize the US from within, Mahershala Ali's character, Geroge "G.H." Scott explains. But the source of the sound is never fully disclosed in either the film or Alam's book.

Ali's character rules out airplanes like the Concorde, a supersonic plane capable of breaking the sound barrier. Meanwhile, Kevin Bacon's survivalist character, Danny, suggests a microwave weapon similar to the one used in Cuba, referencing Havana Syndrome, which US officials believed impacted more than 1,000 US diplomats with symptoms such as migraines, hearing loss, and brain damage.

Bacon's character surmises that the sound came from a microwave radiation weapon, causing one of the characters to vomit violently and his teeth to fall out. Although there haven't been records of people's gums rotting, the film's director, Sam Esmail, told Netflix's Tudum that the sound and its impacts take elements from the real-life reports of the Havana Syndrome.

A report that involved seven US intelligence agencies investigating the source of the mysterious phenomenon ruled that the ailments were unlikely caused by a foreign country. Still, experts haven't ruled out the possibility that the illnesses were caused by a directed-energy weapon (DEW) such as a microwave.

The Intelligence Community Experts Panel on Anomalous Health Incidents released a report in February stating that the Havana Syndrome may have been caused by "pulsed electromagnetic energy, particularly in the radio frequency range."

Military and police agencies around the world are equipped with or are researching DEWs that don't require a solid projectile. These weapons, which could include lasers or high-powered microwaves, can be used to disable drones and missiles or penetrate human skin, according to the US Government Accountability Office. Police have what are essentially loudspeakers that can disperse crowds, and the US military has researched a microwave ray gun that can send messages inside people's heads.

"These weapons can produce force that ranges from deterrent, to damaging, to destructive. Many countries, including the U.S., are researching their use," the GAO said. "Because they use energy instead of bullets or missiles, directed energy weapons could be less expensive per shot and have virtually unlimited firing power."

Esmail's film presents a nightmare scenario in which a destructive DEW is perfected to wreak havoc on a country successfully. Thankfully, experts have said we're not entirely there yet — as far we know.

Below, some real-life examples similar to the mysterious weapon in "Leave the World Behind."

Long-Range Acoustic Device

A Long-Range Acoustic Device (LRAD) acts like a loudspeaker that can emit sounds that reach far distances.

Many US police agencies are equipped with LRADs, according to Acentech, an acoustics consulting firm.

While LRADs can be used to send messages or broadcast, the device has also been used to disperse crowds or protests. In 2011, the New York Police Department used an LRAD to disperse protesters at Zuccotti Park.

At close distances, LRADs can cause nausea, headaches, and permanently damage people's hearing, according to Physicians for Human Rights.

Infrasonic weapons

Infrasonic weapons fall under the same umbrella as LRADs of acoustic devices, but the former is much more sinister.

Unlike LRADs, infrasonic weapons could hypothetically damage a target with a sound inaudible to the human ear.

According to the American Civil Liberties Union, the US military and private companies have been researching infrasonic weapons since the 1990s.

In 2017, US officials believed that such a device was the cause behind the ailments of the Havana Syndrome. However, experts at the time weren't sure if such a device existed.

"There isn't an acoustic phenomenon in the world that would cause those type of symptoms," Seth Horowitz, a neuroscientist and author of the book "The Universal Sense: How Hearing Shapes the Mind," told Business Insider in 2017.

MEDUSA Ray Gun

In 2008, the Sierra Nevada Corporation claimed it could produce a microwave ray gun capable of beaming sounds and even messages inside people's heads.

The device was dubbed MEDUSA or Mob Excess Deterrent Using Silent Audio. According to the company, MEDUSA

Lea Sadovnik, the former vice president of the Sierra Nevada Corporation, told New Scientist in 2008 that the MEDUSA is loud enough to incapacitate a person.

A US Navy report showed that the company built a prototype of the weapon in 2004. The Guardian reported in 2021 that no evidence suggests the gun was taken beyond the prototype phase.